PCBs have been manufactured since 30th and found application for the most part in electrical industry. By late 60th, it has turned out that the environment contained from 300 to 500 thousand tons PCBs (Tarasov V. V. Contamination of the Environment with Polychlorinated Biphenyls and Ways for Minimizing Their Impact, Collection of Scientific Works of RKhTY LXXV Years/Main Scientific Achievements. Moscow, 1996, p.24-41). Annual release of PCBs averages 2000 tons. PCBs penetrate into the environment as the result of failures of PCB-containing equipment and systems, and due to incineration. PCBs penetration into soil is caused by equipment failures or discharges of untreated industrial sewage from plants that employ PCBs in their production run, and by utilization of sludge from irrigated fields. Owing to high absorption power and low degradation ability, polychlorinated biphenyls accumulate in the soil surface layer at a depth of 2-10 cm and in bed sediments. PCBs have been detected substantially in all living nature. PCB is a polytropic poison which affects essentially all body organs and systems. According to data published by the WHO, a human appears to be the most PCB-sensitive creature. PCBs relate to substances of the first hazard group.
Worldwide practice for remediating environment media from PCBs is to use, in general, various physical and chemical methods. In Germany, PCB-contaminated soil is remediated by a method developed by National Research, Canada. According to the method, special dispersion sodium-oil blends are introduced into old landfill sites to assist in chlorine release from PCBs with formation of common salt. (Deckwer W.-D. Weppen P. Review of Methods for Remediating Contaminated Soil and Refused Territories Contaminated with Hazardous Waste.--Chemie-Ingenieur-Technik, 1987, Vol.59, #6, p.457-467).
Gebruder Kemmer/Jng Buro Harbauer Group (Germany) has invented a method for remediation of PCB-contaminated soil, which involves excavation of the soil. The method includes crushing and sieving the soil, the obtained fractions being separately decontaminated with water to which surfactants are added. Flush liquid is supplied to a sewage treatment plant (Schondorf T., Munz K. H. Removal of Polychlorinated Biphenyls from Contaminated Soil.--Chem.Rosch. (Schweiz.), 1988, v.41, #45, s.18).
Kloeckner Oecotec GmbH, Germany, has invented a method for remediation of PCB-contaminated soil, involving washing the soil under a high pressure at a pilot plant. The soil in the form of pieces of up to 10 mm in diameter is ground in a conical water jet. A high pressure of 250 bar in an annular pipe and a great rate of 200-250 m/s promote a complete homogenization and separation of the smallest components and hazardous substances. After the water treatment of the soil, the suspension is separated by one of the following methods: precipitation, cyclone separation, centrifugation, filtration, etc.
Developed in Russia are methods for soil decontamination from PCBs with the aid of a propulsion, plasmatrons (Tarasov V. V. Contamination of the Environment with Polychlorinated Biphenyls and Ways of Minimizing Their Impact. Collection of Scientific Works of RKhTY LXXV years/ Main Scientific Achievements, Moscow, 1996, p.24-41).
All of the above methods suffer a number of essential problems: they are cumbersome, require great investments and disturb the soil ecological equilibrium.
Since late 70th, an ever increasing interest has been expressed in bioremediation methods. It is well known that various bacterial strains and fungi are able to degrade PCBs. They include microorganisms of Pseudomonas genus (Pseudomonas putide for degrading poly-chlorinated biphenyls. U.S. Pat. No.4843009, Int.Cl. C12N 1/12 Application No.866501 filed on May 23, 1986) and fungi of Whit Rod Fungus Phanerochaete chrysosporium (Degradation of 4',4'-Dichlorobiphenyl, 3,Y,4,4'-Tetrachlorobiphenyl, and 2,2',4,4',5,5'-Hexachlorobiphenyl by the White Rot Fungus Phanerochaele chrysosporium. Applied and Environmental Microbiology. 1995. Vol.61, N.11, p.3904-3909), however, the bacteria of Pseudomonas genus are fastidious to nutrient media and storage conditions. Fungi are less convenient in production, and they cause, among other things, a shift in the ecological equilibrium when employed in environment media.